Description

The objective of this technique is to provide an audio (spoken) version of information that is provided visually so that it is possible for people who cannot see to be able to understand audio-visual material.

Since most user agents today cannot merge multiple sound tracks, this technique adds the additional audio information to synchronized media by providing an option which allows users to replace the soundtrack with a new copy of the original soundtrack that has the additional audio description added. This added information focuses on actions, characters, scene changes and on-screen text (not captions) that are important to understanding the content.

Since it is not helpful to have this new information obscure key audio information in the original sound track (or be obscured by loud sound effects), the new information is added during pauses in dialogue and sound effects. This limits the amount of supplementary information that can be added to program.

The soundtrack with the audio description (of visual information) can either be an alternate sound track that the user can choose, or it can be the standard sound track that everyone hears.

Examples

A travelogue of the northeast has additional audio description added during the gaps in the dialogue to let listeners who are blind know what the person is talking about at any point in time.

A video shows a woodpecker carving a nest in a tree. A button within the content allows users to turn the audio description track on or off.

A lecture has audio description added whenever the instructor says things like "and this is the one that is most important." The audio descriptions lets listeners who can not see the video know what "this" is.

A movie file has two audio tracks, one of which includes audio description. Users can choose either one when listening to the movie by selecting the appropriate track in their media player.